diff --git a/source/api_c/tests/test_deeppot_a_ptexpt.cc b/source/api_c/tests/test_deeppot_a_ptexpt.cc
index 064b3b6c7b..59a9832d7b 100644
--- a/source/api_c/tests/test_deeppot_a_ptexpt.cc
+++ b/source/api_c/tests/test_deeppot_a_ptexpt.cc
@@ -169,16 +169,7 @@ TEST_F(TestInferDeepPotAPtExptC, numb_types_spin) {
 
 TEST_F(TestInferDeepPotAPtExptC, type_map) {
   const char* type_map = DP_DeepPotGetTypeMap(dp);
-  std::string type_map_str(type_map);
-  std::istringstream iss(type_map_str);
-  std::vector<std::string> types;
-  std::string token;
-  while (iss >> token) {
-    types.push_back(token);
-  }
-  EXPECT_EQ(types.size(), 2);
-  EXPECT_EQ(types[0], "O");
-  EXPECT_EQ(types[1], "H");
+  EXPECT_STREQ(type_map, "O H");
   DP_DeleteChar(type_map);
 }
 
diff --git a/source/api_cc/src/DeepPotPD.cc b/source/api_cc/src/DeepPotPD.cc
index 51d45a9182..49f409ca4d 100644
--- a/source/api_cc/src/DeepPotPD.cc
+++ b/source/api_cc/src/DeepPotPD.cc
@@ -677,6 +677,7 @@ void DeepPotPD::get_type_map(std::string& type_map) {
 
   std::vector<int> type_map_arr(type_map_size, 0);
   type_map_tensor->CopyToCpu(type_map_arr.data());
+  type_map.clear();
   for (auto char_c : type_map_arr) {
     type_map += std::string(1, char_c);
   }
diff --git a/source/api_cc/src/DeepPotPT.cc b/source/api_cc/src/DeepPotPT.cc
index d69dbb8f82..641a375162 100644
--- a/source/api_cc/src/DeepPotPT.cc
+++ b/source/api_cc/src/DeepPotPT.cc
@@ -452,9 +452,12 @@ template void DeepPotPT::compute<float, std::vector<ENERGYTYPE>>(
     const bool atomic);
 void DeepPotPT::get_type_map(std::string& type_map) {
   auto ret = module.run_method("get_type_map").toList();
+  type_map.clear();
   for (const torch::IValue& element : ret) {
-    type_map += torch::str(element);  // Convert each element to a string
-    type_map += " ";                  // Add a space between elements
+    if (!type_map.empty()) {
+      type_map += " ";
+    }
+    type_map += torch::str(element);
   }
 }
 
diff --git a/source/api_cc/src/DeepPotPTExpt.cc b/source/api_cc/src/DeepPotPTExpt.cc
index c8c1bfcfad..845e804b40 100644
--- a/source/api_cc/src/DeepPotPTExpt.cc
+++ b/source/api_cc/src/DeepPotPTExpt.cc
@@ -947,9 +947,12 @@ template void DeepPotPTExpt::compute<float, std::vector<ENERGYTYPE>>(
     const bool atomic);
 
 void DeepPotPTExpt::get_type_map(std::string& type_map_str) {
+  type_map_str.clear();
   for (const auto& t : type_map) {
+    if (!type_map_str.empty()) {
+      type_map_str += " ";
+    }
     type_map_str += t;
-    type_map_str += " ";
   }
 }
 
diff --git a/source/api_cc/src/DeepSpinPT.cc b/source/api_cc/src/DeepSpinPT.cc
index 5add377045..aa4e05591d 100644
--- a/source/api_cc/src/DeepSpinPT.cc
+++ b/source/api_cc/src/DeepSpinPT.cc
@@ -476,9 +476,12 @@ template void DeepSpinPT::compute<float, std::vector<ENERGYTYPE>>(
     const bool atomic);
 void DeepSpinPT::get_type_map(std::string& type_map) {
   auto ret = module.run_method("get_type_map").toList();
+  type_map.clear();
   for (const torch::IValue& element : ret) {
-    type_map += torch::str(element);  // Convert each element to a string
-    type_map += " ";                  // Add a space between elements
+    if (!type_map.empty()) {
+      type_map += " ";
+    }
+    type_map += torch::str(element);
   }
 }
 
diff --git a/source/api_cc/src/DeepSpinPTExpt.cc b/source/api_cc/src/DeepSpinPTExpt.cc
index 9edd51474b..f5870247f4 100644
--- a/source/api_cc/src/DeepSpinPTExpt.cc
+++ b/source/api_cc/src/DeepSpinPTExpt.cc
@@ -1028,9 +1028,12 @@ template void DeepSpinPTExpt::compute<float, std::vector<ENERGYTYPE>>(
     const bool atomic);
 
 void DeepSpinPTExpt::get_type_map(std::string& type_map_str) {
+  type_map_str.clear();
   for (const auto& t : type_map) {
+    if (!type_map_str.empty()) {
+      type_map_str += " ";
+    }
     type_map_str += t;
-    type_map_str += " ";
   }
 }
 
diff --git a/source/api_cc/tests/test_deeppot_dpa_ptexpt_spin.cc b/source/api_cc/tests/test_deeppot_dpa_ptexpt_spin.cc
index 7d9b04ddc0..a356151c76 100644
--- a/source/api_cc/tests/test_deeppot_dpa_ptexpt_spin.cc
+++ b/source/api_cc/tests/test_deeppot_dpa_ptexpt_spin.cc
@@ -5,6 +5,7 @@
 #include <algorithm>
 #include <cmath>
 #include <fstream>
+#include <string>
 #include <vector>
 
 #include "DeepSpin.h"
@@ -96,6 +97,12 @@ TYPED_TEST(TestInferDeepSpinDpaPtExpt, test_get_use_spin) {
   EXPECT_FALSE(use_spin[2]);  // H has no spin
 }
 
+TYPED_TEST(TestInferDeepSpinDpaPtExpt, type_map) {
+  std::string type_map;
+  this->dp.get_type_map(type_map);
+  EXPECT_EQ(type_map, "Ni O H");
+}
+
 TYPED_TEST(TestInferDeepSpinDpaPtExpt, cpu_build_nlist) {
   using VALUETYPE = TypeParam;
   const std::vector<VALUETYPE>& coord = this->coord;
diff --git a/source/api_cc/tests/test_deeppot_pd.cc b/source/api_cc/tests/test_deeppot_pd.cc
index 6da9ee643b..bede9b11aa 100644
--- a/source/api_cc/tests/test_deeppot_pd.cc
+++ b/source/api_cc/tests/test_deeppot_pd.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <cmath>
 #include <fstream>
+#include <string>
 #include <vector>
 
 #include "DeepPot.h"
@@ -89,6 +90,12 @@ class TestInferDeepPotAPd : public ::testing::Test {
 
 TYPED_TEST_SUITE(TestInferDeepPotAPd, PDValueTypes);
 
+TYPED_TEST(TestInferDeepPotAPd, type_map) {
+  std::string type_map = "stale";
+  this->dp.get_type_map(type_map);
+  EXPECT_EQ(type_map, "O H");
+}
+
 TYPED_TEST(TestInferDeepPotAPd, cpu_build_nlist) {
   using VALUETYPE = TypeParam;
   std::vector<VALUETYPE>& coord = this->coord;
diff --git a/source/api_cc/tests/test_deeppot_pt.cc b/source/api_cc/tests/test_deeppot_pt.cc
index 144ee8da8c..7f527296b1 100644
--- a/source/api_cc/tests/test_deeppot_pt.cc
+++ b/source/api_cc/tests/test_deeppot_pt.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <cmath>
 #include <fstream>
+#include <string>
 #include <vector>
 
 #include "DeepPot.h"
@@ -82,6 +83,12 @@ class TestInferDeepPotAPt : public ::testing::Test {
 
 TYPED_TEST_SUITE(TestInferDeepPotAPt, ValueTypes);
 
+TYPED_TEST(TestInferDeepPotAPt, type_map) {
+  std::string type_map;
+  this->dp.get_type_map(type_map);
+  EXPECT_EQ(type_map, "O H");
+}
+
 TYPED_TEST(TestInferDeepPotAPt, cpu_build_nlist) {
   using VALUETYPE = TypeParam;
   std::vector<VALUETYPE>& coord = this->coord;
diff --git a/source/api_cc/tests/test_deeppot_ptexpt.cc b/source/api_cc/tests/test_deeppot_ptexpt.cc
index 4f90555839..cbf1303633 100644
--- a/source/api_cc/tests/test_deeppot_ptexpt.cc
+++ b/source/api_cc/tests/test_deeppot_ptexpt.cc
@@ -944,8 +944,7 @@ TYPED_TEST_SUITE(TestDeepPotPTExptMetadata, ValueTypes);
 TYPED_TEST(TestDeepPotPTExptMetadata, type_map) {
   std::string type_map;
   this->dp.get_type_map(type_map);
-  EXPECT_NE(type_map.find("O"), std::string::npos);
-  EXPECT_NE(type_map.find("H"), std::string::npos);
+  EXPECT_EQ(type_map, "O H");
 }
 
 TYPED_TEST(TestDeepPotPTExptMetadata, cutoff) {